Exposure timing mechanism



Sept. 17, 1946. s 2,407,800

EXPOSURE TIMING MECHANISM Filed Jan; 26, 1945' I INVENTOR: /0

Patented Sept. 17, 1946 UNITED STATES PATENT OFFICE EXPOSURE TIMINGMECHANISM Roland L. Smith, Belmont, Mass.

Application January 26, 1945, Serial No. 574,662

6 Claims. (Cl. 161-1) This invention relates to exposure timingmechanisms such as are employed in making photographic enlargements andprints by electric light.

A timing mechanism of the class referred to is employed for controllingand operating an electric circuit in which is arranged an electric lampby means of which the enlarging or printing is effected and such adevice is, as a practical matter, essential when a number of prints orenlargements are to be produced from a single negative if uniformity inresults is to be obtained.

A well known type of timing instrument has heretofore been providedwhich comprised a finger-operated rotatable dial, a spring motor foryieldingly urging said dial rotatively in one direction at apredetermined speed, a switch incorporated in the circuit of the lamp,said switch including a resilient contact serving also as a stop forlimiting the rotary movement of the dial under the influence of thespring motor and being normally maintained in open position by the dial,and a finger-engaging stop on the frame or base of the instrument forlimiting the rotary movement of the dial in the opposite direction underthe influence of the finger oi the operator. The dial was made with acircular series of sockets or apertures spaced apart equidistantly atintervals of a predetermined number of seconds, usually five seconds,and in makin an exposure, say for example fifteen seconds, the operatorwould insert his finger in the third aperture or socket in front of thefinger stop and quickly turn the dial clockwise away from the switchuntil movement of his finger and the dial in that direction werearrested by said finger stop whereupon the operator released the dialthereby permitting the spring motor to return the same contraclockwiseto its normal position again at said predetermined speed. At the startof the movement of the dial under the influence of the operators fingerthe resilient contact was released thereby closing the circuit throughthe lamp, and at the completion of the return movement of the dial underthe influence of the spring motor the re-, silient contact was restoredto its normally open position by the dial thereby extinguishing the lampat the expiration of the selected interval of time-fifteen seconds.

An objectionable feature characterizing the above described and otherconstructions heretofore proposed has been that in making manyenlargements or prints from one and the same negative it was necessary,throughout this procedure, for the operator to remember or bear in mindthe length of time, as measured in seconds,

for each exposure since no indication of this.

factor could be derived from the instrument itself,

Another objectionable feature of devices of this class as heretoforeprovided has been that when the dial was constructed with a supplementalseries of holes or sockets, more closely spaced apart than the fingerholes or sockets, for use in effecting exposures differing in time fromthat possible through use of the finger holes, said supplemental holesor sockets were necessarily made too small for the reception of thefinger so that it was necessary for the operator to equip himself with apointed skewer-like accessory instrument such as a pencil, for example,for use within the small supplemental holes when operating the dial.

This invention has for its object to provide an improved timinginstrument of the class described and in particular to obviate the abovenoted objectionable features characterizing devices of this clas asheretofore constructed.

To this end I have provided certain improvements in instruments of theclass indicated as set forth in the following description, the severalnovel features of the invention being separately pointed out and definedin the claims at the close of the description, it being understood,however, that the illustrated embodiments of the invention are to betaken as preferred examples of the latter and that various changes maybe resorted to without departing from my invention as defined in theclaims.

In the accompanying drawing:

Figure 1 is a top plan view of an exposure timing instrument constructedin accordance with this invention.

Figure 2 is a side elevation, partly in section, of the instrument shownin Fig, 1.

Figure 3 is a section on line 3-3 of Figs. 1 and 2.

Figure 4 is a sectional detail relating to th dial of Figs. 1 and 2.

Figure 5 is a partial top plan view of an exposure timing mechanismembodying an alternative form of the invention.

Figure 6 is a side view of the parts shown in Fig. 5.

Figure '7 is a detail hereinafter referred to relating to the embodimentillustrated in Figs. 5 and 6.

The embodiment of my invention illustrated in Figs. 1, 2, 3, and 4 ofthe drawing comprises a molded base 10 of any suitable non-conductingmoldable material, said base being in the form of an inverted cup whichprovides a housing for a spring motor I I and an electric switchcomprising a fixed contact I2 and a resilient contact l3. Contacts I2and [3 are arranged in an electric circuit I4 in series with the usualelectric lamp (not shown) by means of which the photographicenlargements or prints are made from a negative or the like.

Spring motor II is fastened by screws Ila (Fig. 1) to the under side ofthe top wall of base I and includes a vertical shaft 15 which extendsupwardly therefrom loosely through an aperture provided in the top wallof base It! to the exterior thereof where it has fixedly mounted on it acircular molded dial I6 that is formed near its periphery with acircular row of finger holes or sockets I1 disposed concentrically withrespect to the axis of motor shaft I5.

Upon its under side the dial I6 is made with a depending boss IB whichis normally pressed laterally against one side of the upper end of theresilient contact I3 by motor l I so as to hold said contact out ofengagement with the fixed contact I2. The fixed contact I2 is disposedentirely within base I0 where it is fastened by screws to a pad I9(Figs. 2 and 3) forming part of the top wall of the base. The resilientcontact I3 is fastened by screws to another pad Ell forming part of thetop wall of the base and includes a free end portion extending upwardlythrough an aperture ZI formed in the top wall of the base to theexterior of the latter where its upper extremity occupies a position inthe path of the boss I8. 2! serves as a stop to positively limit themovement of contact I3 occasioned by the pressure of the boss againstthe same.

A bracket 22 is fastened by screws to the exterior of base It and theupper end portion of said bracket is made with a lateral finger stopextension 23 which overhangs the marginal portion of dial I6 just abovethe path traversed by the finger-holes or sockets l1 when the dial isrotated on the axis of shaft I5.

The finger-holes or sockets I1 are angularly spaced apart relatively toeach other alike throughout the row a distance equaling the angularmovement of shaft I5 during a predetermined. length of time as measuredby a number of seconds and the angular distance between hole or socket#1 and finger stop 23 is the same.

Assuming this distance between the holes and between hole #1 and stop 23to be equal to the angular displacement of shaft I5 and dial I6 duringan interval of time of five seconds, as in the drawing, it will be clearthat by inserting a finger in either one of the holes I] and turningdial I6 and shaft l5 clockwise until movement of the finger and dial inthat direction is arrested by stop 23 and immediately releasing thedial, then the spring motor will rotate dial I6 and shaft I5contra-clockwise back to their normal positions again and this returnmovement will be effected by motor ll during a period of timecorresponding with the angular distance between the hole that is usedand the stop 23, said period of time being either five seconds or amultiple of five seconds according to the position of said hole.

It will also be clear that during the time that the dial is away fromits normal position switch I2-I3 is closed and the lamp (not shown) ofthe apparatus is lighted. Thus, by using the proper hole or socket I! inoperating the dial One side of this aperture it is possible to providefor an exposure that prevails for a definite measured length of timeappropriate to the characteristics of the particular negative or thelike that is being employed, provided said appropriate time is fiveseconds or a multiple of five seconds.

The above described construction is as heretofore and serves its purposevery well when making a small number of enlargements or prints from asingle negative or the like requiring comparatively long exposures, butwhen making a considerable number of enlargements from one and the samenegative or the like, the operator would often inadvertently use thewrong fingerhole during his repeated operations of the dial because ofthe absence of any means for visually indicating the proper hole to use.Moreover, when operating with a thin negative requiring short accuratelytimed exposures other than of five seconds or a multiple thereof, it wasnot possible to operate the instrument accurately as required exceptthrough the use of the accessory skewer-like implement and therelatively small supplemental holes or sockets, hereinbefore referredto. My improvements, now to be described, obviate these objectionablefeatures characterizing instruments of this kind as heretoforeconstructed and with which I am familiar.

In accordance with this invention I provide the timer mechanism with afinger-operated arm 24 (Fig. 1) of resilient sheet metal disposedradially above, and in close proximity to, the dial I6, said arm beingpivotally secured at its inner end to the upper end of the motor shaftI5 by a screw 25 so that it is normally free to be swung laterallyrelatively to said shaft and the dial in either direction. The outer endof this arm is provided with a depending ratchet tang 26 (Figs. 2 and 4)to cooperate with a composite circular row or series of relatively smallclosely spaced sockets or recesses 21 and 28 formed in the mar-. ginalportion of dial I 6 and disposed concentrically with respect to the axisof shaft I5. Each of these sockets or recesses is adapted to re ceivethe tang 26 as shown in Fig. 4 and provides at one side thereof anabrupt abutment shoulder facing away from stop 23 and adapted to beengaged by one side of tang 25 which is parallel with said shoulder. Theopposite side of tang 25 may be beveled as shown so that the tang mayslide freely over the sockets when arm 24 is rotatively adjusted in thatdirection. The resiliency of arm 24, however, permits the free endthereof to be manually lifted away from the dial when the arm is to beadjusted in either direction.

Each socket 27 of the composite series is cooperatively associated withone of the finger-holes of the dial in that when occupied by the tang ofarm 24 the latter then serves to indicate that the finger-holeassociated with that socket is being used. This is an important functionwhen a number of enlargements or prints are being made from one and thesame negative since it guides the photographer in his operation of thedial and relieves him of the necessity of remembering the particulartiming being employed. Arm 24 likewise serves as an indicator whenengaged with either of the sockets 28.

When the dial occupies its normal position the composite portion of thesupplemental row of sockets 2I28 starts at the finger-stop 23 andextends therefrom contra-clockwise around the marginal portion. of dia1It as far as finger-hole #6, an angular distance corresponding with thedistance traveled by the dial during thirty seconds while being actuatedby spring motor H and throughout this composite portion all of thesockets are spaced apart relatively equidistantly a distancecorresponding with the extent of angular displacement of dial itefiected by motor l l during a one second. period of time.

In making enlargements from a thin negative or the like not only is muchless time required than with a dense or strong one, but much finerregulation or control of the exposure period is necessary with thethinner negative or the like, which is, as Will be clear, obtainablethrough use of arm 24 and the sockets of the composite portion of thesupplemental row, the latter being spaced apart relatively one second.

When using a finger-hole or socket beyond the composite portion of thesupplemental row, which will be the case in producing enlargements froma strong or dense negative or the like, the arm as is set in engagementwith the socket 21 of the appropriate finger-hole and utilized inoperating the dial. With this type of negative or the like regulation ofthe time of exposure to the extent of five seconds or multiple thereofis ordinarily sufficient and this is provided for by the five secondsspacing of the finger-holes that are beyond the composite portion of thesupplemental row.

As shown in Fig. 2 of the drawing the stop extension 23 is disposedabove the path of the dial operating arm 24 so that the latter can, attimes, pass beneath the same.

In starting enlarging operations with a given thin negative the operatorusually makes some preliminary trial exposures by means of the fingerholes I! and after thus ascertaining the approximate time he can thenobtain the exact timing through use of the pawl-like arm 24 and thecomposite row of supplemental sockets 2'l28. In many instances this willavoid the necessity of regulating the intensity of the light.

In the embodiment of the invention illustrated in Figs. 5. 6 and 7 theperiphery of the dial [6a is made throughout its circuit with a circularrow of ratch-like teeth 29 which provide abutment shoulder 39 facingaway from the fixed finger stop 23a, said shoulders co-operating with. avertically resilient pawl-like arm 24a. This arm is pivoted loosely uponthe upper end of the shaft 15 of the spring motor (not shown) and heldin position thereon by a nut 25a having threaded engagement with saidshaft.

The teeth 29 are spaced apart relatively an angular distancecorresponding with the extent of rotary motion imparted to the dial bythe spring motor during one second and within this circular row of teeth29 the dial is formed with a circular row of finger holes or socket-sI'ia which are spaced apart relatively an angular distance correspondingwith the extent of rotary motion imparted to the dial by the springmotor during five seconds, each of said holes or sockets Ila beingdisposed radially opposite one of the abutment shoulders 30a of teeth 29so that the holes of the group or row Ila serve as indicators to guidethe operator in accurately placing the arm 24a in any desired position.

The free end of arm 24a is made with a depending tang 26a (Fig. 7) toco-operate with the teeth 29, said tang being yieldingly held againstthe dial by the resiliency of the arm of which it forms part.

What I claim is:

1. In a timing instrument, the combination of a rotatably supportedswitch-operating dial whose outer marginal portion is made with aconcentric row of finger-sockets angularly spaced apart equidistantly atrelatively large intervals and also with a concentric row ofsupplemental sockets spaced apart equidistantly at smaller angularintervals that subdivide the intervals between said finger-sockets; aradial arm pivotally supported for independent rotative adjustment attimes on the axis of said dial to set said arm in a definitetime-indicating position rela-- tively to said dial; a fixed fingerstop, and means on said arm for engaging one of said supplementalsockets to positively adjust said dial rotatively when said arm is swungby finger pres sure toward said finger-stop.

2. The combination of claim 1 wherein said arm is a resilient member andwherein said lastmentioned means consists of a depending tang providedadjacent to the outer end of said arm and yieldingly held insocket-engaging position by the resiliency of said arm.

3. The combination of claim 1 wherein said finger-stop overhangs saiddial and wherein the outer end portion of said arm is movable with saiddial on a path between the latter and said fingerstop.

4. The combination of claim 1 wherein said supplemental sockets areprovided by a circular row of teeth formed upon the outer marginalportion of the dial.

5. The combination of claim 1 wherein said supplemental sockets areprovided by a circular row of ratchet teeth formed upon the outermarginal portion of the dial, and wherein said arm is a resilientpawl-like member that is maintained in socket-engaging position by itsresiliency.

6. In a timing instrument, in combination, a rotatably supportedswitch-operating dial whose outer marginal portion is made with a row ofrelatively large finger-sockets that are angularly spaced apart atrelatively large intervals concentrically with respect to the axis ofsaid dial, and made also with a concentric row of relatively smallsupplemental sockets spaced apart at smaller angular intervals thatsubdivide the in.- tervals between said finger-sockets; a spring motorhaving a vertically disposed shaft on which said dial is fixed, saidmotor yieldingly maintaining said dial normally at the limit of its r0-tary movement in one direction; a radial fingeroperated arm pivotallymounted loosely upon said shaft for independent rotative adjustmentthereon at times to set said arm in a definite time-indicating positionrelatively to said dial; means carried by said arm for engaging one ofsaid supplemental sockets to positively adjust said dial rotatively whensaid arm is swung by finger pressure in the opposite direction, and afixed finger-stop in the path of the finger for limiting the movement ofthe dial in said opposite direction.

ROLAND L. SMITH.

